In ophthalmic surgery, and in particular in vitreo-retinal surgery, it is desirable to use a wide-angle surgical microscope system to view as large a portion of the retina as possible. Wide-angle objective lenses for such microscopic systems exist, but they require a wider illumination field than that provided by the cone of illumination of a typical fiber-optic probe. As a result, various technologies have been developed to increase the beam spreading of the relatively incoherent light provided by a fiber-optic illuminator. These known wide-angle illuminators can thus illuminate a larger portion of the retina as required by current wide-angle surgical microscope systems.
Current wide-angle illuminators can experience run-away heating that degrades the performance of the illuminator. Run-away heating occurs when the cannula of an illuminator absorbs light from the optical fiber running through the illuminator and, consequently, increases in temperature. As the cannula heats, the optical fiber may begin to deform, causing even more light to be incident on the cannula, increasing the temperature of the cannula further and, hence, increasing the deformation in the optical fiber. This cycle can lead to catastrophic failure of the illuminator.